network/dhcp: disable RapidCommit= by default when AllowList=/DenyList= is specified

network/dhcp: disable RapidCommit= by default when AllowList=/DenyList= is specified

AllowList= and DenyList= filter only DHCPOFFER messages. So, if
RapidCommit= is enabled, then networkd unconditionally accepts a rapid
ACK message even if its sender is filtered out by the lists.

As AllowList=/DenyList= implemented earlier than RapidCommit=, so
enabling RapidCommit= unconditionally by default may break existing
setups that use AllowList=/DenyList=.

Let's disable RapidCommit= by default when AllowList=/DenyList= is
enabled. Still the setting can be enabled by setting explicitly even
AllowList=/DenyList= is also specified.